Origin

The ancient ancestor of deaf also produced Greek tuphlos ‘blind’. It probably referred to general dullness in perception, rather than dullness in any particular sense. Emphatic comparisons include as deaf as an adder and as deaf as a post. The traditional deafness of an adder is based on an image in the Psalms, ‘the deaf adder that stoppeth her ear’. Actually, all snakes are deaf, not just the adder—they ‘hear’ by means of sensors that pick up vibrations in the ground such as footsteps.